Assessment of the effect of tie-ridging on smallholder maize yields in Malawi

Abstract

Tie-ridging is being promoted in Malawi as an on-field rainwater harvesting technique to ensure a maize ( Zea mais L.) crop during a dry or drought year. Resource-poor smallholder farmers are likely to take up tie-ridging if it increases and not decreases maize yield in most years. A numerical study was conducted to calculate the expected maize yield gain due to tie-ridging taking into account the probability of occurrence of drought, dry, normal and wet years (climatic uncertainty). Mean yields due to tie-ridging in drought, dry, normal and wet years at different N levels were derived from observed smallholder maize yield data using a linear nitrogen response model and field-observed retained rainwater amounts in tie-ridged fields. Simulation results indicate that tie-ridging will result in hybrid maize yield gain in a drought year (1050 kg ha −1) and dry year (560 kg ha −1). There will be a hybrid maize yield loss in a normal year (350 kg ha −1) and wet year (700 kg ha −1). For local maize, there will be a yield gain in a drought year (500 kg ha −1), dry year (220 kg ha −1) and normal year (120 kg ha −1). There will be a slight yield loss in a wet year (60 kg ha −1). Considering observed probability of the occurrence of drought, dry, normal and wet years in Malawi, the study reveals that there will be no hybrid maize yield gain in any coming year with tie-ridging. For local maize, the expected yield gain in any coming year was positive (133.3 kg ha −1) but this gain is less than the minimum gain required considering the opportunity cost of labour (142.5 kg ha −1). Thus under the smallholder conditions and climate of Malawi, the expected yield gain in any coming year due to tie-ridging is likely to be minimal and uneconomic.